Methods and devices for minimally invasive spinal fixation element placement

ABSTRACT

Minimally invasive methods and devices for introducing a spinal fixation element into a surgical site in a patient&#39;s spinal column are provided. In one embodiment, a dissection tool is provided for separating muscles along a muscle plane without causing damage to the muscles. The dissection tool can also include a lumen extending therethrough for receiving a guide wire. The tool allows the guide wire to be positioned relative to a vertebra, and once properly positioned, the tool can be removed to allow a spinal anchor to be delivered along the guide wire and implanted into the vertebra.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of application Ser.No. 10/738,130 U.S. Pat. No. 7,527,638, filed on Dec. 16, 2003 andentitled “Methods and Devices for Minimally Invasive Spinal FixationElement Placement,” which is hereby incorporated herein in its entirety.

FIELD OF THE INVENTION

This application relates to tools for use in spinal surgery, and inparticular to minimally invasive methods and devices for introducing aspinal fixation element to one or more spinal anchor sites within apatient's spine.

BACKGROUND OF THE INVENTION

For a number of known reasons, spinal fixation devices are used inorthopedic surgery to align and/or fix a desired relationship betweenadjacent vertebral bodies. Such devices typically include a spinalfixation element, such as a relatively rigid fixation rod, that iscoupled to adjacent vertebrae by attaching the element to variousanchoring devices, such as hooks, bolts, wires, or screws. The fixationelements can have a predetermined contour that has been designedaccording to the properties of the target implantation site, and onceinstalled, the instrument holds the vertebrae in a desired spatialrelationship, either until desired healing or spinal fusion has takenplace, or for some longer period of time.

Spinal fixation elements can be anchored to specific portions of thevertebrae. Since each vertebra varies in shape and size, a variety ofanchoring devices have been developed to facilitate engagement of aparticular portion of the bone. Pedicle screw assemblies, for example,have a shape and size that is configured to engage pedicle bone. Suchscrews typically include a threaded shank that is adapted to be threadedinto a vertebra, and a head portion having a rod-receiving element,usually in the form of a U-shaped slot formed in the head. A set-screw,plug, or similar type of fastening mechanism is used to lock thefixation element, e.g., a spinal rod, into the rod-receiving head of thepedicle screw. In use, the shank portion of each screw is threaded intoa vertebra, and once properly positioned, a rod is seated through therod-receiving member of each screw and the rod is locked in place bytightening a cap or other fastener mechanism to securely interconnecteach screw and the fixation rod.

Recently, the trend in spinal surgery has been moving toward providingminimally invasive devices and methods for implanting spinal fixationdevices. One such method, for example, is disclosed in U.S. Pat. No.6,530,929 of Justis et al. and it utilizes two percutaneous accessdevices for implanting an anchoring device, such as a spinal screw, intoadjacent vertebrae. A spinal rod is then introduced through a thirdincision a distance apart from the percutaneous access sites, and therod is transversely moved into the rod-engaging portion of each spinalscrew. The percutaneous access devices can then be used to apply closuremechanisms to the rod-engaging heads to lock the rod therein. While thisprocedure offers advantages over prior art invasive techniques, thetransverse introduction of the rod can cause significant damage tosurrounding tissue and muscle. Moreover, the use of three separateaccess sites can undesirably lengthen the surgical procedure, andincrease patient trauma and recovery time.

Accordingly, there remains a need for improved minimally invasivedevices and methods for introducing a spinal fixation element into apatient's spine.

BRIEF SUMMARY OF THE INVENTION

Disclosed herein are minimally invasive methods and devices fordelivering a spinal fixation element to one or more spinal anchor sitesin a patient's spinal column. In one embodiment, a minimally invasivesurgical method is provided that includes forming an incision throughtissue located adjacent to a vertebra in a patient's spinal column, andinserting a blunt tip of a tool through the incision while manipulatingthe tool along the muscle plane extending between the incision and thevertebra to separate the muscles. The blunt tip preferably has asubstantially planar configuration, or it includes at least one surfacethat is substantially planar. In an exemplary embodiment, the blunt tipof the tool is adapted to separate the longissimus thoracis andmultifidus muscles. The method can also include inserting a guide wirethrough a lumen extending through the tool. The guide wire is preferablypositioned such that it extends into the vertebra. Once properlypositioned, the tool can be removed leaving the guide wire in positionto receive a spinal implant, such as a spinal anchor, which ispreferably delivered to the vertebra along the guide wire. Theaforementioned method can be repeated to deliver one or more additionalimplants to adjacent vertebrae. A spinal fixation element, such as aspinal rod, can then be delivered along one of the pathways extending toa vertebral body, and it can be coupled to the implant implanted withinthe adjacent vertebrae. In an exemplary embodiment, the fixation elementmay be inserted through one of the pathways in an orientationsubstantially parallel to a longitudinal axis of the first pathway. Incertain exemplary embodiments, the spinal fixation element may bedelivered through a cannula that extends along the pathway from thetissue surface to one of the vertebra.

In another exemplary embodiment, a medical device kit for use in spinalsurgery may include a tissue dissection tool have a blunt member formedon a distal end thereof and adapted to separate muscles along a muscleplane without causing damage to the muscles. The exemplary tissuedissection tool may include a lumen extending therethrough. The kit mayalso include at least one guide wire that is adapted to be disposedthrough the lumen in the tissue dissection tool, and at least one spinalanchor that is adapted to be implanted in a vertebral body. The kit canmay also include at least one cannula that is adapted to provide apathway from a tissue surface to a vertebral body for delivering aspinal anchor to the vertebral body, and/or at least one spinal fixationelement that is adapted to couple to and extend between at least twospinal anchors.

In yet another embodiment of the present invention, a spinal anchor ispercutaneously delivered to a vertebral body having a percutaneousaccess device mated thereto and having a lumen extending therethroughand defining a longitudinal axis. A spinal fixation element is thenadvanced through the lumen in the percutaneous access device in a first,lengthwise orientation in which the fixation element is substantiallyparallel to the longitudinal axis of the percutaneous access device. Thespinal fixation element can then be manipulated to extend in a secondorientation, such that the fixation element is angled with respect tothe first orientation, to position the spinal fixation element inrelation to the spinal anchor. The method can also include the step ofpercutaneously delivering a second spinal anchor to a vertebral bodywith a second percutaneous access device mated thereto. The spinalfixation element thus preferably extends between the first and secondspinal anchors in the second orientation.

In an exemplary embodiment, the percutaneous access device is in theform of an elongate, generally cylindrical tube that is adapted forpercutaneous delivery and that is adapted to mate to a spinal anchor.The tube can include proximal and distal ends with a lumen extendingtherebetween. The lumen is adapted to transport a spinal fixationelement therethrough in a first, lengthwise orientation that issubstantially parallel to a longitudinal axis of the percutaneous accessdevice, and to deliver the spinal fixation element to a spinal anchorsite in a second orientation that is angled with respect to the firstorientation, and more preferably that is substantially parallel to apatient's spinal column. The percutaneous access device can also includeat least one sidewall opening extending from the distal end of theelongate, generally cylindrical tube through at least a portion thereoffor facilitating transition of a spinal fixation element from the firstorientation to the second orientation. In one embodiment, the deviceincludes opposed sidewall openings formed therein adjacent to the distalend thereof. The device can also optionally or alternatively include aguide member formed within the lumen that is adapted to direct a spinalfixation element disposed therein from the first orientation to thesecond orientation. The guide member can be, for example, a sloped shelfformed within the lumen of the percutaneous access device.

In another embodiment of the present invention, a minimally invasivemethod for delivering a spinal fixation element to a spinal anchor sitein a patient's spinal column is provided. The method includes the stepof introducing a spinal fixation element into a lumen of a percutaneousaccess device. The lumen preferably forms a pathway to a spinal anchordisposed in a patient's vertebra. In an exemplary embodiment, thepercutaneous access device has an outer diameter that is substantiallythe same as or less than a largest width of the spinal anchor to whichit is attached. A person skilled in the art will appreciate that theouter diameter of the percutaneous access device can optionally begreater than the outer diameter of the spinal anchor to which it isattached. The method further includes the steps of advancing the spinalfixation element distally through the lumen in a first, lengthwiseorientation that is substantially parallel to a longitudinal axis of thepercutaneous access device, and manipulating the spinal fixation elementinto a second orientation that is substantially parallel to thepatient's spinal column. The spinal fixation element can then bepositioned relative to one or more spinal anchors.

In other aspects of the present invention, a minimally invasive surgicalmethod is provided that includes the steps of making a firstpercutaneous incision in a patient, and creating a first pathway fromthe first percutaneous incision to an anchor site on a first vertebralbody. Preferably, the pathway is a minimally invasive pathway such thatit leads only to a single anchor site, rather than multiple anchorsites. This can be achieved, for example, by a percutaneous accessdevice that has a substantially uniform width from the firstpercutaneous incision to a first anchor site on a first vertebral body.In an exemplary embodiment, the first pathway has a width that issubstantially equal to or less than a width of the first percutaneousincision, and/or that is substantially equal to or less than a width ofa first anchor. The method also includes the steps of placing a firstanchor through the first percutaneous incision, advancing the firstanchor along the first pathway to the single anchor site, and placing afixation element through the first pathway in an orientationsubstantially parallel to a longitudinal axis of the first pathway.

In a further embodiment, a second percutaneous incision can be made in apatient, and a second minimally invasive pathway can be created from thesecond percutaneous incision to a second anchor site on a secondvertebral body. A second anchor is then advanced along the secondpathway to the second anchor site on the second vertebral body.

Additional methods and devices for introducing a spinal fixation elementto one or more spinal anchor sites are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a percutaneous access device coupled toan anchor according to one embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along the longitudinal axis ofthe percutaneous access device shown in FIG. 1;

FIG. 3A is a partially cut-away view of another embodiment of apercutaneous access device having a guide member formed therein;

FIG. 3B is a partially cut-away view of the percutaneous access deviceshown in FIG. 3A having a sleeve disposed there around and a spinalanchor mated thereto;

FIG. 4A is a posterior view of three percutaneous incisions formed inthe thoracolumbar fascia of a patient's back;

FIG. 4B is a posterior view of six percutaneous incisions formed in thethoracolumbar fascia of a patient's back;

FIG. 5A is an end view showing a blunt dissection of the musclessurrounding a patient's vertebra;

FIG. 5B is an end view of the vertebra shown in FIG. 5A showing atechnique using a finger for separating the muscles along the dissectedmuscle plane to gain access to the vertebra;

FIG. 5C is an end view of the vertebra shown in FIG. 5A showing anotherembodiment of a technique using a tool for separating the muscles alongthe dissected muscle plane to gain access to the vertebra;

FIG. 5D is an end view of the vertebra shown in FIG. 5C showing the toolfurther inserted along the dissected muscle plane;

FIG. 5E is an end view of the vertebra shown in FIG. 5C showingplacement of a guide wire through the tool and into the patient'svertebra;

FIG. 5F is a side view of the tool shown in FIGS. 5C-5E;

FIG. 5G is a cross-sectional view of the tool shown in FIG. 5F takenalong line A-A;

FIG. 6 is an end view of the vertebra shown in FIG. 4 showing placementof a guide wire through the incision and into the patient's vertebra;

FIG. 7 is an end view of the vertebra shown in FIG. 6 having anobturator and several dilators disposed over the guide wire to dilatethe tissue and muscles;

FIG. 8 is perspective view of a first spinal anchor implanted in avertebra and having a percutaneous access device coupled thereto andextending through a percutaneous incision formed in the patient's tissuesurface, and a second spinal anchor being implanted into an adjacentvertebra and having a percutaneous access device coupled thereto with adriver tool extending therethrough;

FIG. 9 is a perspective view of two percutaneous access devices attachedto spinal anchors that are disposed within adjacent vertebrae in apatient's spinal column;

FIG. 10 illustrates a method for introducing a spinal fixation elementthrough a partially cut-away view of one of the percutaneous accessdevices shown in FIG. 9;

FIG. 11 is a perspective view of the spinal fixation element shown inFIG. 10 being advanced in toward the spinal anchors using a pusherdevice;

FIG. 12 is a perspective view of the spinal fixation element shown inFIG. 11 after it is fully positioned within receiver heads of theadjacent spinal anchors;

FIG. 13 illustrates a method for introducing a spinal fixation elementthrough a partially cut-away view of the percutaneous access deviceshown in FIGS. 3A and 3B;

FIG. 14 is a perspective view of the spinal fixation element shown inFIG. 13 being advanced toward the spinal anchors using a pusher device;

FIG. 15 is a perspective view of the spinal fixation element shown inFIG. 14 advanced further toward the receiver heads of the adjacentspinal anchors;

FIG. 16 is a perspective view of the spinal fixation element shown inFIG. 15 about to be disposed within the receiver heads of the adjacentspinal anchors; and

FIG. 17 is a perspective view of a compression tool positioned aroundthe percutaneous access devices shown in FIG. 12 and compressing thedevices toward one another, and a closure mechanism being appliedthrough one of the percutaneous access devices to lock the spinalfixation element in relation to the spinal anchor.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides minimally invasive methods and devicesfor introducing a spinal fixation element into a surgical site in apatient's spinal column. In general, the method involves advancing aspinal fixation element in a lengthwise orientation along a minimallyinvasive pathway that extends from a minimally invasive percutaneousincision to a spinal anchor site. In an exemplary embodiment, apercutaneous access device is used to create the minimally invasivepathway for receiving the spinal fixation element and for delivering thefixation element to a spinal anchor site. The spinal fixation element ispreferably inserted through a lumen in the percutaneous access device ina lengthwise orientation, such that the spinal fixation element isoriented substantially parallel to a longitudinal axis of thepercutaneous access device. As the spinal fixation element approaches orreaches the distal end of the pathway, the spinal fixation element canbe manipulated to orient it at a desired angle with respect to thepercutaneous access device, preferably such that the spinal fixationelement is substantially parallel to the patient's spinal column. Thespinal fixation element can then optionally be positioned to couple it,either directly or indirectly, to one or more spinal anchors. Afastening element or other closure mechanism, if necessary, can then beintroduced into the spinal anchor site to fixedly mate the spinalfixation element to the anchor(s).

The methods and devices of the present invention are particularlyadvantageous in that they can be achieved using one or more minimallyinvasive percutaneous incisions for accessing the spinal column. Suchincisions minimize damage to intervening tissues, and they reducerecovery time and post-operative pain. The present invention alsoadvantageously provides techniques for delivering spinal fixationelements and anchors along a minimally invasive pathway, thuseliminating the need to create a large working area at the surgicalsite.

While a variety of devices can be used to perform the methods of thepresent invention, FIGS. 1 and 2 illustrate an exemplary embodiment of apercutaneous access device 12 that is mated to a spinal anchor 50(FIG. 1) to form a spinal implant assembly 10. As shown, the device 12is in the form of a generally elongate, cylindrical tube having an innerlumen 12 c formed therein and defining a longitudinal axis L thatextends between proximal and distal ends 12 a, 12 b. The size of theaccess device 12 can vary depending on the intended use, but it shouldhave a length l that allows the proximal end 12 a of the access device12 to be positioned outside the patient's body, while the distal end 12b of the access device 12 is coupled to, or positioned adjacent to, aspinal anchor, e.g., anchor 50, that is disposed in a vertebra in apatient's spine. The access device 12 is also preferably adapted toprovide a minimally invasive pathway for the delivery of a spinalfixation element, and in particular, the percutaneous access device 12should also be adapted to be implanted through a minimally invasivepercutaneous incision, which is a relatively small incision thattypically has a length that is less than a diameter or width of thedevice being inserted therethrough.

In an exemplary embodiment, the device 12 has an inner diameter d_(i)that is sufficient to allow a spinal fixation element to be introducedtherethrough, preferably in a lengthwise orientation. The inner diameterd_(i) can also optionally be configured to allow a driver mechanism tobe introduced therethrough for applying a closure mechanism to lock thespinal fixation element in relation to a spinal anchor. The outerdiameter d_(o) of the access device 12 can also vary, and it can be thesame as, less than, or greater than an outer diameter d_(r) of thespinal anchor. In the illustrated embodiment, the access device 12 hasan outer diameter d_(o) that is substantially the same as an outerdiameter d_(r) of the spinal anchor, which, as illustrated in FIG. 1, isthe receiver head 52 of a spinal screw 50. This is particularlyadvantageous in that the size of the incision does not need to be anylarger than necessary. The matching outer diameters d_(o), d_(r) of theaccess device 12 and the anchor 50 also allow the access device 12and/or the anchor 50 to be introduced through a cannula. If the accessdevice 12 is mated to the anchor 50, the matching outer diameters d_(o),d_(r) also allows a sleeve or other device to be slidably disposed therearound to prevent disengagement between the access device 12 and theanchor 50. In another, exemplary embodiment, the outer diameter d_(o) ofthe access device 12 can be slightly greater than the outer diameterd_(r) of the spinal anchor. By way of non-limiting example, where areceiver head of the spinal anchor has an outer diameter d, that isabout 13 mm, the access device 12 preferably has an outer diameter d_(o)that is about 15 mm.

The percutaneous access device 12 also preferably includes at least onesidewall opening or slot 14 formed therein, and more preferably itincludes two opposed sidewall openings (only one opening 14 is shown)formed therein and extending proximally from the distal end 12 bthereof. The openings 14 allow a spinal fixation element to beintroduced through the device 12 in a first, lengthwise orientation, inwhich the spinal fixation element is substantially parallel to thelongitudinal axis L of the access device 12. The spinal fixation elementcan then to be manipulated to extend at an angle with respect to thefirst orientation, such that the fixation element extends in a directionsubstantially transverse to the longitudinal axis L of the access device12, for example, in a direction that is substantially parallel to thepatient's spine. Since the length L of the spinal fixation element willnecessarily be greater than the inner diameter d_(i) of the accessdevice 12, the openings 14 allow the spinal fixation element to passtherethrough while being transitioned from the first, lengthwiseorientation to the second orientation. A person skilled in the art willappreciate that the exact position of the spinal fixation element withrespect to the longitudinal axis L will of course vary depending on theconfiguration of the spinal fixation element.

The shape and size of each opening 14 can vary, but the opening(s) 14should be effective to allow movement of the spinal fixation elementfrom the first orientation to the second orientation. In an exemplaryembodiment, the openings 14 extend over about half of the length, orless than half of the length, of the percutaneous access device 12. Theshape of each slot 14 can be generally elongate, and they should eachhave a width w that is sufficient to accommodate the diameter of thespinal fixation element. A person skilled in the art will appreciatethat the percutaneous access device 12 can include any number ofsidewall openings having any shape that is sufficient to allow a spinalfixation element to be moved from the first orientation to the secondorientation.

In another embodiment of the present invention, shown in FIGS. 3A-3B,the percutaneous access device 112 can also optionally include a guidemember 120 formed within the distal end 112 b of the lumen 112 c to helpguide the spinal fixation element from the first orientation to thesecond orientation. The guide member 120 can have a variety ofconfigurations, but it should be effective to guide the spinal fixationelement from the first orientation toward the anchor 50 attached to, orpositioned adjacent to, the access device 112, and optionally towardanchor(s) implanted in adjacent vertebrae. In an exemplary embodiment,as shown, the guide member 120 is in the form of a sloped shelf formedwithin the inner lumen 112 c of the access device 112 and preferablypositioned opposite to a single sidewall slot 114 formed in the accessdevice 112. The sloped shelf 120 can vary in shape and size depending onthe type of fixation element being used and/or the geometry of theaccess device. In use, as the leading end of a spinal fixation element,such as a spinal rod, contacts the shelf 120, the shelf 120 begins todirect the spinal fixation element into the second orientation, therebycausing the spinal fixation element to extend in a direction that issubstantially transverse to the axis L of the device 112, and that ispreferably substantially parallel to the patient's spinal column. Thespinal fixation element can then be manipulated to position it inrelation to one or more spinal anchors, as will be discussed in moredetail below.

Referring back to FIG. 1, in use, the percutaneous access device 12 canbe adapted to attach to a spinal anchor 50. Accordingly, the distal end12 c of the percutaneous access device 12 can include one or more matingelements 18 formed thereon or therein for engaging the anchor 50.Suitable mating elements include, for example, threads, a twist-lockengagement, a snap-on engagement, or any other technique known in theart, and in an exemplary embodiment the mating elements are formed onopposed inner surfaces of the distal end 12 b of the access device 12. Asleeve 100 (partially shown in FIG. 3B) or other device, preferablyhaving sidewall openings (not shown) that correspond with the sidewallopenings 14 formed in the percutaneous access device 12, can also beplaced over the percutaneous access device 12, and optionally over theimplant 50 as well, to prevent disengagement of the access device 12from the implant 50 during use. Exemplary techniques for mating thepercutaneous access device 12 to an anchor are disclosed in a patentapplication entitled “Percutaneous Access Devices and Bone AnchorAssemblies,” filed concurrently herewith. A person skilled in the artwill appreciate that a variety of other techniques can be used toremovably mate the percutaneous access device to an anchor.

For reference purposes, FIG. 1 illustrates an exemplary spinal anchorfor use with the methods and devices of the present invention. A personskilled in the art will appreciate that a variety of anchors can be usedwith the devices and methods of the present invention, including, forexample, spinal screws, hooks, bolts, and wires. FIG. 1 illustrates aspinal screw that includes a distal, bone-engaging portion, e.g., athreaded shank 54, and a proximal, U-shaped, receiver head 52 that isadapted to seat a spinal fixation element, preferably a spinal rod (notshown). The threaded shank 54 can be fixedly attached to the receiverhead 52 to form a monoaxial screw, or alternatively the shank 54 can beconfigured as a polyaxial screw, as shown, that is rotatably disposedthrough an opening formed in the distal end of the receiver head 52 toallow rotation of the shank 54 with respect to the receiver head 52. Avariety of techniques can be used to allow rotation of the head 52 withrespect to the shank 54.

FIGS. 4A-17 show a minimally invasive method of implanting a spinalfixation element. While the method is shown and described in connectionwith the percutaneous access device 12 and spinal screw 50 disclosedherein, a person skilled in the art will appreciate that the method isnot limited to use with such devices, and that a variety of otherdevices known in the art can be used. Moreover, while only two accessdevices 12, 12′ and two anchors 50, 50′ are shown in FIGS. 4-14, themethod of the present invention can be performed using any number ofaccess devices and anchors. The method can also be performed using onlysome of the method steps disclosed herein, and/or using other methodsknown in the art.

The procedure preferably begins by forming a minimally invasivepercutaneous incision through the tissue located adjacent to the desiredimplant site. While the location, shape, and size of the incision willdepend on the type and quantity of spinal anchors being implanted, FIG.4A illustrates three midline minimally invasive percutaneous incisions62 a-c formed on one side of three adjacent vertebra in thethoracolumbar fascia in the patient's back, and FIG. 4B illustratesthree additional midline minimally invasive percutaneous incisions 62d-f formed on the opposite side of the three adjacent vertebra in thethoracolumbar fascia in the patient's back. Each incision 62 a-f is astab incision that has a diameter of about 10-20 mm in diameter, howeverthis can vary depending on the procedure. In an exemplary embodiment,each incision 62 a-f has a diameter that is equal to or less than alargest diameter of the anchor and/or the percutaneous access devicebeing inserted therethrough.

While probably not necessary, once the percutaneous incisions 62 a-f areformed, blunt finger dissection can optionally be used, as shown inFIGS. 5A-5B, to separate the longissimus thoracis LT and multifidusmuscles M, thereby exposing the facet and the junction of the transverseprocess and superior articular process.

FIGS. 5C-5E illustrate another exemplary technique for separating thelongissimus thoracis and multifidus muscles using a blunt tool 200,which is shown in more detail in FIGS. 5F-5G. Referring first to FIGS.5F-5G, the tool 200 generally includes a rigid elongate shaft 202 havingproximal and distal ends 202 a, 202 b. The shaft 202 also includes alumen 202 c extending therethrough between the proximal and distal ends202 a, 202 b for receiving a guide wire, such as a k-wire. The lumen 202c may be sized to receive a guidewire 202 c delivered through the lumen202 c. The proximal end 202 a may include a handle 204 formed therein tofacilitate grasping of the tool 200. The handle 204 can have virtuallyany shape and size. For example, as shown in FIGS. 5F-5G, the handle 204in the exemplary embodiment has a generally elongate cylindrical shapeand it includes ridges 204 a formed thereon to facilitate gripping ofthe device.

The distal end 202 b of the tool 200 includes a blunt member 206 formedthereon. The blunt member 206 may be adapted, e.g., sized and shaped, toseparate muscles along a muscle plane while concomitantly minimizingtrauma to the separated muscles. While the shape of the blunt member 206can vary, in an exemplary embodiment, as shown, the blunt member 206 hasa substantially elongate rectangular shape with opposed front and backsurfaces 206 a, 206 b. The width between the front and back surfaces 206a, 206 b may taper or decreases in a distal direction such that thedistal-most width w_(b2) is less than the proximal-most width W_(b1).Such an exemplary configuration facilitates insertion of the bluntmember 206 between tissue, e.g., muscle, to allow the tissue to beseparated. The width w_(s) extending between opposed side edges of thefront and back surfaces 206 a, 206 b can also vary, but in an exemplaryembodiment, as shown, the width w_(s) remains constant along the lengthof the front and back surfaces 206 a, 206 b.

While not shown, the tool 200 can also optionally include an inner tubedisposed within the elongate shaft 202 for preparing the vertebra. Inparticular, the inner tube can be slidably disposed within the elongateshaft 202 to allow the inner tube to be moved distally into bone tocreate a divot in the vertebra, thereby preparing the bone for an awl ortap. The tool 200 can also optionally serve as a drill guide. Inparticular, the elongate shaft 202 can have an inner diameter that isadapted to receive a drill therethrough to guide the drill toward andinto the vertebra. The shaft 202 also serves as a protective cannula forthe drill, inhibiting contact between the drill and the musclessurrounding the tool 200. A person having ordinary skill in the art willappreciate that the tool 200 can have a variety of other configurations,and that the tool 200 can be adapted for a variety of other uses.

Referring now to FIGS. 5C-5E, the exemplary tool 200 is shown in use. Asshown, after the percutaneous incisions 62 a-f are formed, as previouslydescribed, the blunt member 206 of the dissection tool 200 may beinserted through an incision 62. The incision 62 may be deep enough toallow the fat layer between the longissimus thoracis and multifidusmuscles to be located. Once located, the tool 200 may be manipulated toseparate or split the longissimus thoracis and multifidus muscles,thereby exposing the facet and the junction of the transverse processand superior articular process. Once the tool 200 is positioned adjacentto or against the vertebra 60, as shown in FIG. 5D, a guide wire, e.g.,a k-wire 64, can be inserted through the lumen 202 c in the tool 200 toposition a distal end of the k-wire 64 at or within the vertebra 60, asshown in FIG. 5E. Fluoroscopy or other imaging may be used to facilitateproper placement of the k-wire 64. The tool 200 can then be removed fromthe k-wire 64, leaving the k-wire 64 to serve as a guide for variousother devices, which will be described in more detail below. Thisprocedure can be repeated at each incision 62 a-f to facilitateplacement of multiple spinal anchors.

Where tool 200 is not used, a guide wire, e.g., k-wire 64, can beimplanted, either prior to or after formation of the incision, at eachspinal anchor implant site. As shown in FIG. 6, the k-wire 64 preferablyextends between the muscles and into the vertebra at the desired entrypoint of the spinal anchor. Fluoroscopy can be used to facilitate properplacement of the k-wire 64.

The opposed ends of the incision can then be dilated to provide apathway for delivery of a spinal anchor to each implant site. FIG. 7illustrates dilation at one end of the incision 62 using an obturator 66a having several dilators 66 b, 66 c of increasing size placed thereover. The dilators 66 b, 66 c are delivered over the obturator 66 a andk-wire 64 to essentially stretch the skin around the incision 62 and toexpand the pathway to the anchor site.

Once the incision 62 is dilated to the proper size, an anchor can bedelivered to each anchor site, as shown in FIG. 8. This proceduretypically involves preparation of the vertebra 60 using one or more bonepreparation instruments, such as drills, taps, awls, burrs, probes, etc.While not always necessary, one or more cannulae can be used to providea pathway from the incision 62 to the anchor site for insertion of thebone preparation instruments and/or the anchor. In an exemplaryembodiment, a relatively small cannula is used to introduce bonepreparation instruments into the surgical site. The incision 62 can thenbe further dilated, and the small cannula can be replaced with a largercannula that is adapted to receive or mate to the anchor.

Once the vertebra 60 is prepared, a spinal anchor can be implanted ateach implant site. An access device 12, 12′ can be mated to each anchor50, 50′ after insertion of the anchor 50, 50′ into bone 60, 60′, butmore preferably each percutaneous access device 12, 12′ is attached tothe anchor 50, 50′ prior to insertion of the anchor 50, 50′ into bone60, 60′ to provide a passageway for a driver tool for driving the anchor50 into bone 60, 60′. FIG. 8 illustrates anchor 50 implanted in a firstvertebra 60 and having access device 12 attached thereto. While notshown, the anchor 50 is preferably cannulated to allow the k-wire 64 toextend through the anchor 50 and the access device 12 to guide thedevices 50, 12 toward the implant site. FIG. 8 further illustrates asecond anchor 50′ having an access device 12′ mated thereto. As shown,the screw 50′ is about to be implanted in a second vertebra 60′ that isadjacent to the first vertebra 60. Once the screw 50′ is positionedadjacent to the vertebra 60′, a driver tool 90 can be positioned throughthe access device 12′ and coupled to the receiver head 52′ of the screw50′ to drive the screw 50′ into the vertebra 60′.

In another embodiment, a sleeve can be placed over each access device12, 12′, either prior to or after the devices 12, 12′, 50, 50′ areimplanted, to prevent the devices 12, 12′ from becoming disengaged fromthe anchors 50, 50′ to which they are attached. The sleeve 100, which ispartially illustrated in FIG. 3B, is preferably in the form of a cannulathat has substantially the same configuration as each access device 12,12′. The use of a sleeve is particularly desirable where the accessdevices 12, 12′ utilize pin members that engage corresponding detentsformed on an outer surface of each screw head 52, 52′, as the sleevewill prevent the pin members from becoming disengaged from the detents.The sleeve can also optionally serve as an access device, allowingaccess devices 12, 12′ to be detached and removed from the anchors 50,50′.

After the anchors 50, 50′ are implanted, a spinal fixation element 70 isdelivered to the anchor site. This can be achieved by introducing thespinal fixation element 70 through one of the percutaneous accessdevices 12, 12′ that is attached to the anchor 50, 50′, or through someother percutaneous access device that provides a pathway to theanchor(s) 50, 50′. As shown in FIG. 9, a spinal fixation element, e.g.,a spinal rod 70, is introduced into device 12 in a first, lengthwiseorientation, such that the spinal fixation element 70 is substantiallyparallel to the longitudinal axis L of the access device 12. Where thefixation element has a curved orientation or it has some otherconfiguration, it is understood that the fixation element is in the“substantially parallel” orientation when it is positioned lengthwisethrough the percutaneous access device.

The spinal fixation element 70 is then moved distally toward the distalend 12 b of the percutaneous access device 12, as shown in FIGS. 10 and11. Movement of the spinal fixation element 70 can be achieved using amanipulator device 80. The manipulator device 80 can have a variety ofconfigurations, but it should be effective to allow controlled movementof the fixation element 70. A person skilled in the art will appreciatethat a variety of other techniques can be used to guide the spinalfixation element 70 through the percutaneous access device 12 and toposition the spinal fixation element 70 in relation to one or moreanchors 50, 50′. Moreover, the spinal fixation element 70 can have avariety of configurations to facilitate insertion through a percutaneousaccess device. By way of non-limiting example, a patent applicationentitled “Flexible Spinal Fixation Elements,” and filed concurrentlyherewith, discloses a spinal fixation element that can be flexed as itis passed through a percutaneous access device, thereby allowing thespinal fixation element to transition from the first orientation to thesecond orientation. The application also discloses techniques fordelivering the spinal fixation element along a guide wire or cable, thuseliminating the need for a manipulator device. Other spinal fixationelements suitable for use with the present invention, in addition tomechanical and flexible fixation elements, include, for example,inflatable fixation elements such as those disclosed in U.S. PatentPublication No. 2002/0068975, entitled “Formable Orthopedic FixationSystem with Cross Linking” by Teitelbaum et al., U.S. Patent PublicationNo. 2002/0082600, entitled “Formable Orthopedic Fixation System” byShaolian et al., and U.S. Patent Publication No. 2002/0198526, entitled“Formed In Place Fixation System With Thermal Acceleration” by Shaolianet al., each of which are hereby incorporated by reference in theirentirety.

Referring now to FIGS. 11 and 12, as the spinal fixation element 70approaches the distal end 12 b of the access device 12, the spinalfixation element 70 can be manipulated to cause the spinal fixationelement 70 to assume a second orientation that is different from thefirst orientation, and more preferably that is substantially parallel tothe patient's spinal column and/or transverse to the first orientation.It is understood that the angle of the fixation element 70 in the secondorientation will vary depending on the type of fixation device beingimplanted, as well as the orientation of the access device 12, which canvary throughout the surgical procedure since the access device 12 can bepositioned at several angles with respect to the patient's spinalcolumn.

During transition of the spinal fixation element 70 from the firstorientation to the second orientation, a leading end of the spinalfixation element 70 should be subcutaneously positioned. Where theaccess device 12 includes slots or openings (only one opening 14 isshown), the opening(s) 14 can be used to facilitate movement of thespinal fixation element 70 into the second orientation as they willallow the spinal fixation element 70 to extend therethrough duringrotation. This may not be necessary, however, depending on the length ofthe openings 14, the length of the spinal fixation element 70, and/orthe configuration of the spinal fixation element 70. As shown in FIGS.11 and 12, only the leading end 70 a of the spinal fixation element 70exits the percutaneous access device 12 through one of the openings 14.

Referring to FIG. 12, manipulation of the spinal fixation element 70 iscontinued until the spinal fixation element 70 is positioned in relationto one or more spinal anchors. Depending on the type of spinal anchorused, the fixation element can be positioned to be directly orindirectly mated to the spinal anchor. As shown in FIG. 12, the fixationelement 70 is fully seated in the receiver heads 52, 52′ of the adjacentspinal anchors 50, 50′. The manipulator device 80, if used, can then beremoved from the access device 12.

In another embodiment, the percutaneous access device 112 shown in FIGS.3A and 3B can be used to facilitate introduction of a spinal fixationelement into a surgical anchor site. As previously stated, access device112 includes a guide member 20 formed therein to direct the spinalfixation element 70 from the first orientation to the secondorientation. This is illustrated in FIGS. 13-16. As shown, as the spinalfixation element 70 is moved distally to come into contact with theguide member 120, the guide member 120 causes the spinal fixationelement 70 to rotate and extend toward the opening 114 in thepercutaneous access device 112. As a result, the spinal fixation element70 is directed into the second orientation, whereby it can be positionedin or adjacent to the receiver heads 52, 52′ of the adjacent spinalimplants 50, 50′.

Referring back to FIG. 12, once the spinal fixation element 70 is fullyseated in the receiver heads 52, 52′ of the adjacent spinal anchors 50,50′, the pusher shaft 80, if used, can then be removed or detached fromthe spinal fixation element 70, and a closure mechanism can be appliedto one or both receiver heads 52, 52′ to retain the spinal fixationelement 70 therein. In an exemplary embodiment, however, a compressiontool 100 is used to compress the access devices 12, 12′ toward oneanother prior to applying a closure mechanism to each anchor 50, 50′.The closure mechanism(s) can, however, be partially applied beforecompression.

An exemplary compression tool 300 is shown in FIG. 17, and in general itincludes opposed arms 302, 304 that are pivotally coupled to one anotherat a substantial mid-point thereof such that each arm 302, 304 includesa distal portion 302 b, 304 b that is adapted to be disposed around apercutaneous access device 12, 12′, and a proximal, handle portion 302a, 304 a. The device 300 can also include a fulcrum (not shown) that isdisposed between the arms 302, 304 to facilitate controlled movement ofthe arms 302, 304 with respect to one another. In use, the distalportion 302 b, 304 b of each arm 302, 304 is placed around an accessdevice 12, 12′, preferably around the distal end 12 b, 12 b′ of eachdevice 12, 12′ and/or around the head 52, 52′ of each anchor 50, 50′.The proximal, handle portions 302 a, 304 a are then brought toward oneanother to move the access devices 12, 12′ toward one another,preferably while maintaining relative spacing therebetween, as shown inFIG. 17.

Once properly positioned, a closure mechanism can be applied, preferablyvia the access devices 12, 12′, to each anchor head 50, 50′ to retainthe spinal fixation element 70 within the receiver heads 52, 52′. Avariety of closure mechanisms and tools for delivering closuremechanisms are known in the art and they can be used with the presentinvention. By way of non-limiting example, FIG. 13 illustrates drivertool 90 disposed through access device 12 for applying a closuremechanism, such as a set screw, to the receiver head 52 of the spinalanchor 50 to lock the spinal fixation element 70 with respect to thespinal anchor 50. This step can be repeated for the adjacent spinalanchor(s).

A person skilled in the art will appreciate that the spinal fixationelement 70 does not need to be directly attached to each anchor 50, 50′,and that it can be indirectly attached to the anchors 50, 50′ using, forexample, a band clamp, or slotted or offset connectors.

Once the fixation element 70 is secured in relation to the implants 50,50′, the access devices 12, 12′ can be removed from the implants 50,50′, leaving only minimally invasive percutaneous incisions in thepatient where each access device 12, 12′ was introduced. This isparticularly advantageous in that it reduces the amount of trauma causedto the patient, and it minimizes the damage to muscle surrounding thesurgical site.

As previously stated, a person skilled in the art will appreciate thatthe method can be performed in any sequence using any of the steps.Moreover, the access devices of the present invention can be used todeliver multiple spinal fixation elements simultaneously orsequentially, and/or to perform a variety of other surgical proceduresnot illustrated or described herein.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

1. A minimally invasive surgical method, comprising: forming an incisionthrough tissue located adjacent to a vertebra in a patient's spinalcolumn; identifying a muscle plane between muscles; inserting asubstantially planar blunt tip of a tool through the incision whilemanipulating the blunt tip along the muscle plane extending between theincision and the vertebra to separate the muscles and thereby form apathway; placing a spinal screw through the first pathway, the spinalscrew having a percutaneous access device mated thereto; advancing thespinal screw with the percutaneous access device mated thereto along thepathway to the vertebra; and placing a fixation rod lengthwise throughthe pathway in an orientation substantially parallel to a longitudinalaxis of the pathway.
 2. The method of claim 1, wherein the longissimusthoracis and multifidus muscles are separated.
 3. The method of claim 1,wherein the incision is a minimally invasive percutaneous incision. 4.The method of claim 1, further comprising inserting a guide wire througha lumen extending through the tool.
 5. The method of claim 4, whereinthe guide wire extends into the vertebra.
 6. The method of claim 4,further comprising removing the tool from the guide wire such that theguide wire extends between the incision and the vertebra.
 7. The methodof claim 6, wherein the spinal screw is delivered along the guide wireand implanted in the vertebra.
 8. The method of claim 6, furthercomprising inserting a plurality of dilators over the guide wire todilate tissue surrounding the guide wire.
 9. The method of claim 8,further comprising inserting a cannula over the plurality of dilatorsand removing the dilators.
 10. The method of claim 9, wherein the spinalscrew is delivered through the cannula.
 11. A minimally invasivesurgical method, comprising: making a first incision in a patient;inserting a blunt tip of a tool through the first incision andmanipulating the blunt tip to create a first pathway from the firstincision, between a muscle plane, to a first site on a first vertebralbody; advancing a guide wire through the tool to position a distal endof the guide wire adjacent the first site; removing the tool andadvancing a first implant along the guide wire to the first site on thefirst vertebral body; and placing a fixation element through the firstpathway in an orientation substantially parallel to a longitudinal axisof the first pathway, and coupling a portion of the fixation element tothe first implant.
 12. The method of claim 11, further comprising:making a second incision in a patient; inserting a blunt tip of a toolthrough the second incision and manipulating the tool to create a secondpathway from the second incision, between a muscle plane, to a secondsite on a second vertebral body; and advancing a guide wire through thetool to position a distal end of the guide wire adjacent to the secondsite.
 13. The method of claim 12, further comprising removing the tooland advancing a second implant along the second pathway to the secondsite on the second vertebral body.
 14. The method of claim 13, furthercomprising placing a fixation element through the first pathway andcoupling a portion of the fixation element to the first and secondimplants.
 15. The method of claim 14, wherein the fixation element isinserted through the first pathway in an orientation substantiallyparallel to a longitudinal axis of the first pathway.
 16. The method ofclaim 11, wherein a percutaneous access device is coupled to the firstimplant as the first implant is advanced along the guide wire to thefirst site on the first vertebral body.